The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
This invention relates to object detection systems in general and in particular to radar systems having exceptionally high immunity to interference.
Since an essential part of modern warfare is the location of targets or reference marks by means of a detection system such as radar, it is appropriate to presume that any potential enemy will take steps, such as the creation of man-made interference by countermeasures device to prevent the effective use against himself of detection equipment. Such countermeasures devices may assume various forms such as an inverse gain repeater, a range gate pull-off repeater, chaff, radar decoys, image frequency jammers, and other forms, each of which assumes the nature of an isotropic scatterer because of the necessity in such a countermeasures device for wide angle coverage and broad frequency bandwidth. The usual form of target, such asian aircraft, is not an isotropic scatterer hence apparatus capable of differentiating between a signal obtained from a complex target and a signal obtained from an isotropic scatterer can permit the continuance of reliable detection and tracking for fire control and guidance purposes despite the presence of such countermeasures.
An additional type of countermeasures device described in copending application Ser. No. 755,361, filed coincidentally, entitled. xe2x80x9cSecurity Devicexe2x80x9d xe2x80x9cproduces a tiltxe2x80x9d of the front phase of the return signal from the target to confuse the usual radar system which determines the direction of a distant energy return object by sensing the phase front of return energy. The phase front xe2x80x9ctiltxe2x80x9d is produced by the emission of signals from the vicinity of an energy reflective object which corresponds in characteristics and timing to the normal radar echo signals produced by the energy reflective object but which are of greater amplitude and, which is very important, produce a composite phase front of return energy which is not perpendicular to the direct path between the energy reflective object and the receiver antenna, being xe2x80x9ctiltedxe2x80x9d with respect to such direct path. The result when such a signal is received at the radar system is to cause the antenna of the radar system to orient itself in a direction such that its major axis of directivity is perpendicular to the phase front of energy as received but which no longer corresponds to the true direction to a distant energy reflective object. This causes complete loss of tracking accuracy.
The present invention seeks to counteract such a phase front tilting countermeasure as well as the isotropic scatterer form of countermeasure by deliberately producing a tilt in the phase front of the transmitted energy. This causes the phase front tilting countermeasure itself to become a tracking signal source for the radar system whereas the isotropic scatterer types of countermeasures are insensitive to the phase front of transmitted energy and hence produce return signals which may be distinguished from a true radar echo return signal which is highly sensitive to the phase front of transmitted energy.
It is accordingly an object of the present invention to provide a radar system having a high degree of immunity to countermeasures devices.
Another object of the present invention is to provide a radar system which is immune to phase front tilt countermeasures devices.
Another object of the present invention is to provide a radar system having immunity to countermeasures devices and which has improved operational characteristics for conventional object location operations.